1. Field of the Invention
This invention relates to a contact-free surface mensuration method and apparatus which provides data to digital computers and more particularly apparatus capable of high data rates so that movement of the surface, such as occurs with live subjects, can be accommodated.
2. The Prior Art
Surface mensuration apparatus have been limited to use on inanimate subjects because of methods that are inherently slow. Examples are U.S. Pat. No. 4,089,608 and No. 4,373,804 which use mechanical scanning or mechanical error correction. To make a high resolution measurement of the surface of a living subject, such as the human head, measurement rates greater than 10,000 points per second are required. At these high rates image data can be collected before movement of the subject causes excessive distortion in the image.
A second problem with optical non-contact apparatus is shadowing of the light beam or obstruction of the sensor's view by features of the subject surface. U.S. Pat. No. 4,089,608 is an example which has this limitation.
Recently, in the referenced related application, a high speed method using multiple sources of illumination for alleviating shadowing has been disclosed. The geometry of this apparatus has several limitations.
The multiple data for the same surface point are obtained at different times, resulting in registration error if a line surface moves with respect to the mounting means between measurement times.
The multiple data for the same surface point must all be stored in memory, increasing the complexity and time required for storage.
For surfaces which have points lying behind the point of intersection of the light planes the sensor incorrectly identifies the light sources resulting in error.